Question

Vapour Pressure of Solutions of Non-Volatile or Volatile Solutes

31.686 g of a non-volatile solute is dissolved in 460.0 g of water.
The solute does not react with water nor dissociate in solution.
Assume that the resulting solution displays ideal Raoult's law behaviour.
At 10°C the vapour pressure of the solution is 9.055 torr.
The vapour pressure of pure water at 10°C is 9.209 torr.
Calculate the molar mass of the solute (g/mol).

See example 17.1 on pp865-6 of Zumdahl ''Chemical Principles'' 7th ed.

Now suppose, instead, that 31.686 g of a volatile solute is dissolved in 460.0 g of water.

This solute also does not react with water nor dissociate in solution.
The pure solute displays, at 10°C, a vapour pressure of 0.921 torr.
Again, assume an ideal solution.
If, at 10°C the vapour pressure of this solution is also 9.055 torr.
Calculate the molar mass of this volatile solute.